Spatial and Temporal Dynamics of Potentially Toxic Cyanobacteria in the Riverine Region of a Temperate Estuarine System Altered by Weirs

Abstract

Abstract:The effects of weirs on fish and other biological communities have garnered considerable study, whereas the effects of weirs on community composition of toxic cyanobacteria have not yet been well documented. In this study, temporal and spatial variations in species composition and the abundance of potentially toxic cyanobacteria were investigated in the riverine regions of the temperate Youngsan River estuary, where two weirs have recently been constructed. Four stations were sampled 0.5 m below the surface monthly along the channel of the upper river from May 2014 to April 2015 to explore cyanobacterial composition and abundance, while physicochemical and biological parameters were measured to elucidate possible mechanisms controlling these dynamics. Two stations were located upstream at free-flowing sites, and the other stations were located downstream at impounded sites near the weirs. Twenty-eight cyanobacterial species were identified, seven of which were potentially toxic: Microcystis sp., M. aeruginosa, M. flos-aquae, Dolichospermum sp., Aphanocapsa sp., Oscillatoria sp. and Phormidium sp. Microcystis sp. was the most abundant in June 2014 at the lowest station near the weir. Meanwhile, Phormidium sp. occurred at low abundance throughout the study period, except during the winter months, when its abundance was elevated. The interactive forward selection method highlighted dissolved inorganic nitrogen and zooplankton abundance as explanatory variables for this observed variation, but their effects on cyanobacterial growth are unclear. However, temperature was the major determinant for the temporal variation in cyanobacterial populations. Cluster analysis showed that the downstream stations near the weirs had a high similarity of potentially toxic cyanobacteria. Significantly higher abundance, especially of Microcystis sp., was also recorded at the impounded sites suggesting that the presence of weirs might affect variations in toxic cyanobacterial communities.

Co-varying Environmental Conditions Control the Spatiotemporal Dynamics of Microcystis aeruginosa and Botryococcus braunii in a Freshwater Ecosystem

“…These conditions favored Cyanophyta, rather than Chlorophyta, species diversity at 22°C. Considering that the impact is species-specific, previously reported data regarding the role of winter conditions in a harsh eutrophic environment are inconsistent (Malazarte et al, 2017). The current study indicated the great ability of Chlorophyta and Cyanophyta to tolerate a wide temperature range, forming monospecific and/or multispecific dense blooms in no particular season.…”

Impact of river-reservoir hybrid system on zooplankton community and river connectivity

“…In other studies, before and after weir construction, native shes were more sensitive to disturbance than exotic species in RRHSs (Jo et al, 2019), and riverine wetlands used as habitats and refuge for zooplankton also decreased (Im et al, 2020). A cyanobacteria community, a phytoplankton community, was also shown to be affected by weir construction (Malazarte et al, 2017).…”

“…Weirs are lateral structures installed on rivers that change the running water ecosystem into a lentic ecosystem (becoming an RRHS) and hinder water ow, which is a core process of the river ecosystem, thus changing the structure of the food webs (Jo et al, 2019). Environmental changes and community changes induced by 4LRPs have been investigated in many studies (Malazarte et al, 2017;Jo et al, 2019;Im et al, 2020). However, there are few studies on the deterioration of the connection between zooplankton communities induced by 4LRPs.…”